Allophone

In phonetics, an allophone is one of several similar speech sounds (phones) that belong to the same phoneme. A phoneme is an abstract unit of speech sound that can distinguish words: That is, changing a phoneme in a word can produce another word. Speakers of a particular language perceive a phoneme as a distinctive sound in that language. An allophone is not distinctive, but rather a variant of a phoneme; changing the allophone won't change the meaning of a word, but the result may sound non-native, or be unintelligible. (There is debate over how real, and how universal, phonemes really are. See phoneme for details.)

Every time a speech sound is produced, it will be slightly different from other utterances. Only some of the variation is significant (i.e., detectable or perceivable) to speakers. There may be complementary allophones which are distributed regularly within speech according to phonetic environment, as well as notable free variants, which are a matter of personal habit or preference. Not all phonemes have significantly different allophones.

In the case of complementary allophones, each allophone is used in a specific phonetic context and may be involved in a phonological process.

A tonic allophone is sometimes called an allotone, for example in the neutral tone of Mandarin.

Examples in English vs. other languages

For example, [ph]
as in pin and [p]
as in spin are allophones for the phoneme /p/
in the English
language because they cannot distinguish words (in fact,
they occur in complementary
distribution). English speakers treat them as the same
sound, but they are different: the first is aspirated
and the second is unaspirated
(plain). Plain [p]
also occurs as the p in cap[khæp],
or the second p in paper[pʰeɪ.pɚ].
Chinese
languages treat these two phones differently; for example
in Mandarin, [p]
is written b in Pinyin
and [ph]
is written p; different letters are required because
they distinguish words.

Besides, there are many different allophonic processes in English, like lack of plosion, nasal plosion, partial devoicing of sonorants, complete devoicing of sonorants, partial devoicing of obstruents, lengthening and shortening vowels, dentalisation and retraction.

Aspiration – strong explosion of breath. In English a voiceless plosive that is p, t or k is aspirated whenever it stands as the only consonant at the beginning of the stressed syllable.

Lack of plosion – In English a plosive (p, t, k, b, d, g) has no plosion when it is followed by another plosive or an affricate inside words or across word boundary.

Nasal plosion – In English a plosive (p, t, k, b, d, g) has nasal plosion when it’s followed by nasal, inside a word or across word boundary.

Partial devoicing of sonorants – In English a non vocalic sonorant that is not a vowel (j, w, l, r, m, n, ŋ) is partially devoiced when it follows a voiceless sound within the same way inside a word.

Complete devoicing of sonorants – In English a non vocalic sonorant is completely devoiced in the position of aspiration, when they follow a voiceless plosives (p, t, k) standing as the first consonant at the beginning of the stressed syllable.

Partial devoicing of obstruents – in English language a voiced obstruent is partially devoiced next to a pause or next to a voiceless sound, inside a word or across its boundary.

Dentalisation – in English t, d, n, l become dental before voiced and voiceless English ‘th’ sound.

Retraction – in English t, d, n, l are retracted before r.

Because the choice of allophone is seldom under conscious control, people may
not realize they exist. English-speaking people may become
aware of the difference between two allophones of the phoneme
/t/,
namely unreleased [t̚] and aspirated [tʰ], if they contrast the pronunciations
of the following words:

Night rate:
[ˈnʌɪt̚.ɹʷeɪt̚]

Nitrate:
[ˈnaɪ.tʰɹ̥eɪt̚]

If a flame is held before the lips while these words are spoken,
you may notice that it flickers more during aspirated nitrate
than during unaspirated night rate. The difference
can also be felt by holding the hand in front of the lips.
For a Mandarin speaker, to whom /t/ and /tʰ/ are separate phonemes, the English
distinction is much more obvious than it is to the English
speaker who has learned since childhood to ignore it.

Allophones of English /l/ may be noticed
if the 'light' [l] of leaf[ˈliːf] is contrasted with the 'dark' [ɫ] of feel[ˈfiːɫ]. Again, this difference
is much more obvious to a Turkish speaker, for whom /l/ and /ɫ/ are separate phonemes, than to an
English speaker, for whom they are allophones of a single
phoneme.

Representing a phoneme with an allophone

Since phonemes are abstractions of speech sounds, not the sounds themselves, they have no direct phonetic transcription. When they are realized without much allophonic variation, a simple (i.e. 'broad') transcription is used. However, when there are complementary allophones of a phoneme, so that the allophony is significant, things become more complicated. Often, if only one of the allophones is simple to transcribe, in the sense of not requiring diacritics, then that representation is chosen for the phoneme.

However, there may be several such allophones, or the linguist may prefer greater precision than this allows. In such cases a common convention is to use the "elsewhere condition" to decide which allophone will stand for the phoneme. The "elsewhere" allophone is the one that remains once the conditions for the others are described by phonological rules. For example, English has both oral and nasal allophones of its vowels. The pattern is that vowels are nasal only when preceding a nasal consonant within the same syllable; elsewhere they're oral. Therefore, by the "elsewhere" convention, the oral allophones are considered basic; nasal vowels in English are considered to be allophones of oral phonemes.

In other cases, an allophone may be chosen to represent its phoneme because it is more common in the world's languages than the other allophones, because it reflects the historical origin of the phoneme, or because it gives a more balanced look to a chart of the phonemic inventory. In rare cases a linguist may represent phonemes with abstract symbols, such as dingbats, so as not to privilege any one allophone.